Boosting devices such as turbochargers and superchargers utilize compressors to provide greater amounts of air to the combustion chamber during operation. Consequently, engine power may be increased while reducing emissions. However, during certain engine operating conditions the turbocharger compressor may experience undesirable phenomenon such as surge and choke. Compressor surge occurs when the pressure gradient across the impeller exceeds a threshold, such as during low speed and high throttle conditions. Conversely, compressor choke occurs when the impeller reaches or approaches a maximum flowrate, such as during high speed conditions.
Attempts have been made to alleviate compressor surge through the use of a ported shroud in the compressor. One example approach is shown by Chen in U.S. Pat. No. 7,475,539. Therein, a shrouded port bypassing a section of the compressor impeller is provided to recirculate air around the impeller during surge conditions and increase airflow to the impeller during choke conditions. Thus, Chen's shrouded port in essence increases the compressor's flow range and efficiency.
However, the inventors herein have recognized potential issues with such systems. As one example, during surge conditions the airflow through Chen's ported shroud has a high temperature due to the elevated pressure of the recirculated air. Consequently, the efficiency of the compressor decreases during surge conditions, thereby decreasing engine efficiency. Moreover, elevated temperatures in the compressor can increase the likelihood of thermal degradation of compressor components.
Other attempts have been made to use variable geometry compressors in an attempt to improve the compressor's flow range and efficiency. However, variable geometry compressor are costly and may be susceptible to malfunction due to the complexity of the adjustable geometry components.
Attempts have also been made to provide variable inlet guiding vanes to improve low end compressor efficiency. However, compressor employing variable inlet guiding vanes usually suffer from flow capacity limitations during high end compressor operation.
In one example, the issues described above may be addressed by a compressor including an impeller receiving air from an inlet passage, a housing surrounding the impeller, a bypass passage including a first passage port positioned downstream of a leading edge of the impeller and a second passage port positioned upstream of the leading edge, and a liquid coolant passage extending through a section of the housing at least partially surrounding the bypass passage. In this way, intake air flowing through the bypass passage can be cooled to increase the pressure of the intake air flowing through the compressor, thereby increasing compressor efficiency.
As one example, the liquid coolant passage may circumferentially surround a section of the bypass passage. In this way, the airflow through the compressor can be cooled to a greater extent, enabling additional cooling benefits to be achieved by the cooling system.
It should be understood that the summary above is provided to introduce in simplified form a selection of concepts that are further described in the detailed description. It is not meant to identify key or essential features of the claimed subject matter, the scope of which is defined uniquely by the claims that follow the detailed description. Furthermore, the claimed subject matter is not limited to implementations that solve any disadvantages noted above or in any part of this disclosure.